var Stats = function () {

  var mode = 0;

  var container = document.createElement('div');
  container.style.cssText = 'position:fixed;top:0;left:0;cursor:pointer;opacity:0.9;z-index:10000';
  container.addEventListener('click', function (event) {

    event.preventDefault();
    showPanel(++mode % container.children.length);

  }, false);

  //

  function addPanel(panel) {

    container.appendChild(panel.dom);
    return panel;

  }

  function showPanel(id) {

    for (var i = 0; i < container.children.length; i++) {

      container.children[i].style.display = i === id ? 'block' : 'none';

    }

    mode = id;

  }

  //

  var beginTime = (performance || Date).now(), prevTime = beginTime, frames = 0;

  var fpsPanel = addPanel(new Stats.Panel('FPS', '#0ff', '#002'));
  var msPanel = addPanel(new Stats.Panel('MS', '#0f0', '#020'));

  if (self.performance && self.performance.memory) {

    var memPanel = addPanel(new Stats.Panel('MB', '#f08', '#201'));

  }

  showPanel(0);

  return {

    REVISION: 16,

    dom: container,

    addPanel: addPanel,
    showPanel: showPanel,

    begin: function () {

      beginTime = (performance || Date).now();

    },

    end: function () {

      frames++;

      var time = (performance || Date).now();

      msPanel.update(time - beginTime, 200);

      if (time >= prevTime + 1000) {

        fpsPanel.update((frames * 1000) / (time - prevTime), 100);

        prevTime = time;
        frames = 0;

        if (memPanel) {

          var memory = performance.memory;
          memPanel.update(memory.usedJSHeapSize / 1048576, memory.jsHeapSizeLimit / 1048576);

        }

      }

      return time;

    },

    update: function () {

      beginTime = this.end();

    },

    // Backwards Compatibility

    domElement: container,
    setMode: showPanel

  };

};

Stats.Panel = function (name, fg, bg) {

  var min = Infinity, max = 0, round = Math.round;
  var PR = round(window.devicePixelRatio || 1);

  var WIDTH = 80 * PR, HEIGHT = 48 * PR,
    TEXT_X = 3 * PR, TEXT_Y = 2 * PR,
    GRAPH_X = 3 * PR, GRAPH_Y = 15 * PR,
    GRAPH_WIDTH = 74 * PR, GRAPH_HEIGHT = 30 * PR;

  var canvas = document.createElement('canvas');
  canvas.width = WIDTH;
  canvas.height = HEIGHT;
  canvas.style.cssText = 'width:80px;height:48px';

  var context = canvas.getContext('2d');
  context.font = 'bold ' + (9 * PR) + 'px Helvetica,Arial,sans-serif';
  context.textBaseline = 'top';

  context.fillStyle = bg;
  context.fillRect(0, 0, WIDTH, HEIGHT);

  context.fillStyle = fg;
  context.fillText(name, TEXT_X, TEXT_Y);
  context.fillRect(GRAPH_X, GRAPH_Y, GRAPH_WIDTH, GRAPH_HEIGHT);

  context.fillStyle = bg;
  context.globalAlpha = 0.9;
  context.fillRect(GRAPH_X, GRAPH_Y, GRAPH_WIDTH, GRAPH_HEIGHT);

  return {

    dom: canvas,

    update: function (value, maxValue) {

      min = Math.min(min, value);
      max = Math.max(max, value);

      context.fillStyle = bg;
      context.globalAlpha = 1;
      context.fillRect(0, 0, WIDTH, GRAPH_Y);
      context.fillStyle = fg;
      context.fillText(round(value) + ' ' + name + ' (' + round(min) + '-' + round(max) + ')', TEXT_X, TEXT_Y);

      context.drawImage(canvas, GRAPH_X + PR, GRAPH_Y, GRAPH_WIDTH - PR, GRAPH_HEIGHT, GRAPH_X, GRAPH_Y, GRAPH_WIDTH - PR, GRAPH_HEIGHT);

      context.fillRect(GRAPH_X + GRAPH_WIDTH - PR, GRAPH_Y, PR, GRAPH_HEIGHT);

      context.fillStyle = bg;
      context.globalAlpha = 0.9;
      context.fillRect(GRAPH_X + GRAPH_WIDTH - PR, GRAPH_Y, PR, round((1 - (value / maxValue)) * GRAPH_HEIGHT));

    }

  };

};

export default Stats;
